Questions and Answers
What is the approximate percentage of air found in soil?
30%
Which of the following is NOT a significant factor in the formation of a particular type of soil?
Cultural practices
What process is responsible for decreasing the size of rocks without altering their composition?
Mechanical (physical) weathering
Which constituent of soil is responsible for breaking down rocks at the Earth's surface?
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What type of weathering involves the weakening and disintegration of rocks by plants, animals, and microbes?
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Which of the following processes is responsible for breaking down rock minerals by altering their chemical composition?
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Which of the following is NOT one of the most common chemical weathering processes?
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In most cases, the minerals found in soils are different from those found in the parent rocks. True or false?
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Which of the following soil properties affects air and water movement in the soil?
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What does FAO stand for in the context of soil classification in Ethiopia?
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Which of the following is NOT one of the major groups of soils in Ethiopia discussed in the text?
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Study Notes
Soil Composition and Formation
- Soil is a delicate, varied composition of mineral particles, organic matter, and living organisms in dynamic equilibrium.
- Soil composition consists of: • Weathered mineral materials (45%) • Organic matter (5%) • Air (20-30%) • Water (20-30%)
- Soil formation is a long-term process that takes thousands of years to form a single stratum of soil.
- Factors influencing soil formation: • Parent material • Climate • Topography • Living organisms • Time
Weathering and Soil Formation
- Weathering disintegrates inorganic substances (rocks) of soils through: • Mechanical (physical) weathering • Biological weathering • Chemical weathering
- Types of weathering: • Mechanical weathering: physical disintegration, differential stresses, and abrasion • Biological weathering: weakening and disintegration of rock by plants, animals, and microbes • Chemical weathering: modification of chemical and mineralogical composition of weathered material
Soil Properties
- Soil has two basic properties: • Physical properties: influenced by composition and proportion of major soil components • Chemical properties: interaction of chemical constituents among soil particles and retained water
- Physical properties include: • Texture • Structure • Porosity
- Chemical properties include: • Availability of minerals • Electrical conductivity • Soil pH
Soil Types in Ethiopia
- Soils of Ethiopia are derived from crystalline, volcanic, and Mesozoic sedimentary rocks.
- FAO has identified 18 soil associations in Ethiopia at a scale of 1:2,000,000.
- Six major groups of soils in Ethiopia, characterized by: • Environmental conditions (parent material, climate, topography, formation) • Characteristics (chemical and physical properties) • Agricultural suitability (texture) • Occurrence
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